You have to look at any EV incentive policy from a big-picture point of view. If you want to push the population at large towards adapting EVs and build up EV infrastructure along the way, you need to provide incentives for a large swath of the population. PHEVs are also eligible for this rebate and are a great entrypoint for a large section of the population into EVs. A lot of people here turn their nose up in disdain over PHEVs but I'm all for them existing because EVs haven't achieved parity with ICE vehicles just yet to match everyone's personal use cases. Tons of people who would never have considered EVs, are going to be incentivized to go the PHEV route due to the credits. Others who were on the fence will make the plunge with EVs due to the significant incentives. Unreasonable amounts of means testing is also going to hurt the overall goal. You want people who tend to buy cars and upgrade cars to also be incentivized to spend their money on EVs. That's one less ICE vehicle on the road every time someone makes that decision. It's one thing if you were subsidizing Model S Plaid and Roadsters, but it is perfectly reasonable to subsidize cars like the MY and M3 (along with competitors in the same price range) because these are high-volume cars and your best bet of quickly transforming the make-up of America's vehicles.
Calling Tesla and other EVs as "luxury" vehicles also is a bit short-sighted. The more Teslas and other EVs that cost $50K+ that are sold now, the more used EVs there will be on the market in a few years at affordable prices. The more the market appetite for EVs grow and infrastructure along with it, the more it enables manufacturers to push ahead with trying to reduce costs. A $30K EV is not very far away. And it's not like large numbers of Americans don't buy $40K+ cars every year. This is not an overnight transformation. But it gets the ball rolling in a pretty big way to help with this transition.
Edit - Also, by making a large portion of the population eligible for these credits when buying their next cars, this also pressures other car makers to stop dragging their feet and really invest in EVs at volume. Again, from a big-picture, multi-year view, these are all good things that this type of policy will bring about. It's easy to get caught up in a myopic view of Person X who has way too much money got a tax-credit to buy a Model Y, but that is missing the forest for the trees imo.